The invention relates to filters wherein the elements forming the filtration apertures enlarge during reversals of the filtrate flow.
Filtration barriers, particularly filter screens and meshes, require a periodic reversal of the fluid flow through the barrier (termed a back-wash) to clear the barrier of captured and entrapped solid particles. The back-washed filtration barrier is then ready for a further filtration. Attention is directed to WO 98/23357 (Obst).